Lancing devices are typically handheld units that permit users to draw blood for testing and diagnostic purposes. These devices include a housing with a piercing aperture, a lancet and a firing mechanism. The firing mechanism typically includes a spring or other biasing means which can be cocked either by insertion of the lancet or by pulling a cocking handle, for example. Once the lancing device is cocked, it is placed against the user's skin, often the fingertip. The user can then press a trigger to actuate the firing mechanism, which momentarily drives the sharp tip of lancet through the piercing aperture to puncture the user's skin and draw blood. When the lancing operation is complete, the user can press a second actuator to eject the lancet for removal and disposal. A consideration in the design of both lancets and lancet devices is to minimize parts and thus minimize cost of production.
Another consideration in the design of lancets is to minimize the discomfort experienced by users during the lancing process. To this end, some lancing devices include mechanisms to adjust the distance that the lancet sharp protrudes through the piercing aperture, thus regulating the depth that the lancet penetrates the user's skin. In some cases, these depth adjustment mechanisms include adjustable stops that limit the forward movement of the lancet during firing. In other cases, a lancet holder is moved axially within a lancing device housing to move the needle closer to or farther away from the piercing aperture, thus adjusting penetration depth.
Lancing devices can draw blood from a user's fingertip or other body part. A fingertip is a good testing site because it contains a large number of blood vessels and it is therefore easy to draw an adequate quantity of blood from the fingertip. However, fingertips are also sensitive and users who must frequently draw blood samples may experience discomfort from repeated sampling of the fingertips. Therefore, some users also perform lancing operations on parts of the body, and this is known as alternate site testing or alternate site incision, also known as “AST.”
To effectively draw blood from an alternate site, it is helpful to have the needle penetrate the skin more deeply. It is also helpful to have a relatively wide piercing aperture. A wider piercing aperture acts as an expression ring by allowing the skin to pucker into the aperture's opening and by compressing a wider area of skin around the incision. When skin protrudes through the aperture into the housing, it is also more deeply penetrated by the lancet.
Another consideration in the design of lancing devices is to avoid accidental needle pricks when inserting and removing lancets from the lancing device. To this end, lancets include safety features such as frangible tabs which cover the needle sharp prior to insertion in the lancing device. Once the lancet is inserted, the use can break off and remove the frangible tab. Some lancets also include sleeves coaxially mounted to the main body of the lancet. The sleeve can be positioned so that it protectively encloses the needle sharp. During the lancing operation, the main body of the lancet slides through the sleeve to expose the lancet sharp. After removal of the lancet, however, the sleeve can be locked in its protective position, reducing the likelihood that a person handling the use lancet will prick himself or herself.
Another consideration in the design of lancing systems is the ease with which a lancet can be inserted into the lancing device. It is known that when a lancet is inserted into a lancing device, the force of the insertion can be used to cock the device. However, if the device is already cocked, and a lancet was to be inserted, there is some risk that the device would discharge during the insertion process and the user would be accidentally pricked. It is also known to insert the lancet into the lancet device when the cap of the device is removed.